Neurosurgery sometimes involves inserting an instrument through a burr hole or other entry portal into a subject's brain toward a target region of the brain. Because of the precision needed to reach the target, while avoiding nearby structures that are often critical to brain function, stereotactic instrument guidance is sometimes provided. In one such technique, a stereotactic headframe is mounted about the patient's skull. A trajectory guide is mounted to the headframe to provide an instrument-guiding trajectory through the burr hole and aimed toward the target. In another technique (sometimes referred to as “frameless stereotaxy”), a trajectory guide is locally mounted directly to the skull in or about the burr hole. The skull-mounted trajectory guide also provides an instrument-guiding trajectory through the burr hole and aimed toward the target. In either technique, an image-guided workstation may be used to provide navigational guidance to the neurosurgeon, such as by displaying preoperative images of the subject to assist the neurosurgeon in planning or performing the procedure.
Among other things, the present inventors have recognized that a neurosurgeon using a trajectory guide to introduce an instrument to a target may want to confirm that the instrument has actually reached the depth of the desired target. For these and other reasons, which will become apparent upon reading the following detailed description and viewing the drawings that form a part thereof, the present inventors have recognized an unmet need for trajectory guide systems, devices, and methods allow confirmation that an instrument being introduced has actually reached the desired target.